Vibratory conveying, feeding, screening and the like systems have been driven by different vibratory generating apparatus and have been used in many different industries for many years. A typical vibratory generating apparatus was shown and described in my U.S. Pat. No. 4,025,419, where electric motors drive eccentric weights for producing vibrational forces for a sand reclaiming apparatus. The eccentric weights are fixed relative to the axis of the motor so that an unusually heavy unbalanced load is placed on the motors at start up.
Improved variable rate vibratory generating apparatus were subsequently developed and patented as shown in my U.S. Pat. Nos. 3,358,815 and 4,495,826. In the '815 patent, an apparatus is provided where at start up the unbalanced weight is close to the center of rotation (short radius arm) so that the load on the motor is minimized. As the motor builds up speed, the apparatus provides for moving the weight outward (increases the radius arm) relative to the center of rotation thereby increasing the unbalance and thus increasing the amplitude of vibration. The '815 structure permitted varying the amplitude of vibration to the most desired and most efficient setting.
U.S. Pat. No. '826 provides a structure where a fixed eccentric weight is balanced by a movable eccentric weight so that at start up little or no unbalance exists and, therefore, there are little or no vibratory forces generated. When the motor, which may or may not be a variable speed type, reaches the desired speed, the movable eccentric weight is moved to a desired position to create the desired degree of unbalance and the desired vibratory forces for the associated equipment.
Each of the prior or existing systems has shortcomings. Apparatus like U.S. Pat. No. 4,025,419 each motor and eccentric has one amplitude of vibration which is non-variable and which placed heavy start up loads on the motor. Apparatus like U.S. Pat. Nos. 3,358,815 and 4,495,826 are more complicated to build and maintain and require external controls to increase the amplitude of vibration once the motor is up to speed, which of course placed less stress on the motor and consumes less power during start up.